The invention relates to a method and an apparatus for the manufacture of clinker of mineral raw materials, such as cement clinker, according to the wet process during which a slurry of wet-ground mineral raw materials and water is preheated, dried, burned and sintered to clinker in a kiln plant, for instance a rotary kiln plant.
The wet process being a well known method for clinker manufacture since clinker production became industrialized has been described in numerous places, and Duda: "Cement Data Book", 3rd edition, sections 19.3 and 19.4 (Bauverlag GmbH, Wiesbaden und Berlin 1985) therefore serves as a general example of a citation in that respect. Although today the manufacture of clinker takes place preferably in dry process plants quite a number of wet process plants are still in use for instance both in the USA and in Great Britain due to the existence of easily available wet raw materials combined with the still fairly good running economy of wet plants in spite of other, clearly evident disadvantages of such plants.
One of these disadvantages is their very high specific sulfur dioxide (SO.sub.2) emission compared to other more modern kiln types. Previously this SO.sub.2 -emission was not hardly considered at all, but already the present strict environmental air pollution regulations and especially the far more stricter regulations to be expected in the future might force wet process plants, such as cement production plants, in the countries in question either to close down or to be provided with expensive smoke gas desulfurization systems or to convert the wet process into a dry or semi-dry process thereby facilitating the desulfering of the smoke gases which may apart from the closing down situation causes a considerable increase of the production costs.
Various processes for removing oxides and other acidic gases from the gas from e.g. power plants and other kiln plants are known and referred to for instance in U.S. Pat. No. 4,555,390 which discloses a desulfuring method by means of a tubular reaction chamber acting as a so called gas suspension absorber coupled--seen in the direction of the movement of the kiln exit gases--after a kiln and fed with a dry recirculated powder such as fly ash, an absorption agent such as calcium oxides and water to the bottom of the reaction chamber for desulfuring through absorption the SO.sub.2 in the kiln exit gases during the passage of the latter up through the chamber.
In this method the kiln exit gases from whatever type of kiln are treated in the gas suspension absorber irrespective of the process in the kiln proper and the desulfuring equipment as such therefore clearly represents an extra installation cost of the plant.